1. Field of the Invention
The present invention relates to a positioning device for positioning an object and an associated device manufacturing method.
2. Description of the Related Art
Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device may be used to generate a desired circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist).
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
Typically, a lithographic apparatus is equipped with a plurality of positioning devices. These devices may be applied to accurately position or displace an object table provided with a patterning device or a substrate or to accurately position an object, such as an optical element, which may comprise lens elements or mirrors.
In order to accurately position or displace the object or object table, the actuators are electromagnetic actuators or linear motors, planar motors, piezo-electric actuators, pneumatic or hydraulic actuators.
Often, these actuators are not directly attached to the object or object table that requires accurate positioning. Instead, a connector comprising a resilient member is arranged between the first actuator (or actuators) and the object. As an example, the actuators or the drive arrangement may be connected to the object or object table by means of leaf springs. One reason for applying these connections is to avoid the mechanical connection between the drive arrangement and the object or object table becomes overdetermined. By applying such resilient members (e.g. leaf springs) between the actuator and object table mechanical stresses in the object or object table due to thermal deformations of the actuator may be reduced or avoided. It should be noted that the resilient member may not be introduced on purpose or as a separate item between the first actuator and the object, but may represent a part of the mechanical construction having a lack of constructional stiffness as a consequence of limitations in the mechanical design.
A drawback of the positioning device as described is that the finite stiffness between the drive arrangement and the driven object causes a relative displacement between the object that is driven and the drive arrangement due to deformation of the resilient member. This deformation may affect the positioning accuracy of the object or the time necessary to obtain the required accuracy (i.e. settle time). Such a deformation of the resilient member may, for example, comprise a compression or elongation.